ABSTRACT Type I interferons (IFNs) are cytokines, that are important regulators of immune responses and are downregulated in human cancers, including skin cancer. Solar ultraviolet (UV) radiation is a proven environmental carcinogen, and exposure to solar radiation contributes to UVB induced immunosuppression. The formation of cyclobutane pyrimidine dimers (CPD) are a major cause of UVB induced immunosuppression. Our studies show that mice lacking the type I IFN receptor 1 (IFNAR1) had decreased repair of UVB induced CPD in the skin and increased immunosuppression. We hypothesize that type I IFNs will repair UVB induced DNA damage and prevent UVB induced immunosuppression in mice. To test our hypothesis, we will use mice, lacking IFNAR1, which is critical for signaling of type I IFNs; and XPA, that are deficient in the gene responsible for DNA repair. Using these unique mouse models, we will be able to (1) determine if regulatory T- cells develop in IFNAR1 knockout mice after exposure to UVB; and (2) evaluate whether regulation of UVB induced DNA damage by type I IFNs has any implications on immunosuppression in mice.